Biotic function of charcoal in pine ecosystems of the inland Northwest

Tom Miles

Biotic function of charcoal in pine ecosystems of the inland Northwest
MacKenzie, M. Derek*,1, DeLuca, Thomas 1, Gundale, Michael1, Kurth, Valerie1, Brimmer, Rachel1, 1 College of Forestry and Conservation, Missoula, Montana, USA, Ecological Society of America, Annual Meeting,Portland,OR 2004

ABSTRACT- Charcoal is ubiquitous in many forest soils as a byproduct of wildland fire, however, no studies have effectively addressed the role charcoal plays in soil biochemical transformations. In the work reported here, we describe a series of studies directed at determining the influence of charcoal on net mineralization and nitrification in ponderosa pine forest ecosystems. Laboratory and greenhouse incubations were conducted in which field collected charcoal was added to soils in combination with various litter and N amendments. Forest floor samples were collected from sites not known to have experienced any fire for over 120 years. Samples were excavated to a depth of 5 cm into the mineral soil and placed in plastic trays in the greenhouse. These samples were then treated with 50 kg ha-1 glycine and 1000 kg ha-1 of charcoal. Soil samples were also collected from field sites with varied fire history (2 to 120 years since fire) and analyzed for nitrifier activity in the presence and absence of charcoal. Charcoal was found to directly influence net nitrication in most laboratory assays, however, it was found to have no consistent effect on net N mineralization. Soil samples amended with extracts of Arctostaphylos uva-ursi were found to have high levels of phenolic compounds and reduced N mineralization and nitrification. This effect was greatly eliminated by the addition of charcoal to the soils. Charcoal both reduced the presence of total phenolics and increased net nitrification. When charcoal was added directly to aerated soil slurries, a significant increase in nitrifier activity was observed within a 24 hour period. This indicates that charcoal likely has a direct influence on nitrifier activity as opposed to an indirect effect associated with changes in soluble organic matter via surface sorption.

Key words: Nitrification, Phenolic compounds, Charcoal, Microbial biomass

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